Amplifying circuit arrangement



Oct. .26, 1948. G. SIEZEN AMPLIFYING CIRCUIT-ARRANGEMENT Filed Oct. 18, 1946 INVENTOR GERRIT I. SIEZEN Bv %%7 AGENT Patented Get. 26, 1948 AMPLIFYING CIRCUIT ARRANGEMENT Gerrit Ean Siezen, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust ompany,-lllartford, Conn, as trustee Application ()ctober 18, 1946, Serial No. "104,122 in the Netherlands August 3, 1945 Section 1, Public Law 690, August 8, 194.6 Patent expires August 3, 1965 i Claims.

The invention relates to the acoustical reproduction of electrically transmitted oscillations, and it particularly pertains to reproduction in a plurality of overlapping acoustical ranges by means of a plurality of acoustical reproducers. For such'purposes it is known to use'the circuitarrangement shown in Fig. l, which comprises an amplifying tube l, the anode circuit of which includes two transformers T1 and T2 which feed a high pitched sound and a bass tone loudspeaker Li and L2 respectively, The primary inductance of T1 is given a comparatively low value and a condenser C is connected in parallel with the primary winding of T2. Thus it is ensured that the transformer T1 transmits the frequency-band ft (Fig. 2) of the high pitched sounds, the trans former T2 transmitting the frequency-band ii of the bass tones; these bands partly overlap each other in the proximity of the separating fre quency f5. For instance, if the lowest and the highest frequency of the oscillations to be reproduced amount to 50 and 15,000 C./S., the separating frequency is may, for example, amount to about 30-0 C./S. The circuit-arrangement should be proportioned to be such that the total frequency characteristic curve becomes flat, 1. e. that at a control Voltage which is constant for all frequencies and set up at the grid of tube l, the total acoustic power radiated by the loudspeakers is constant throughout the frequency range to be reproduced (equalization condition). Furthermore, in order to take full advantage of the amplifying tube l it is required that the total anode impedance throughout the frequency range should be practically real and independent with respect to frequency, and should have a definite value prescribed for the tube (adaptation condition).

The invention is based on the recognition that, if the electro-acoustic outputs of the loudspeakers are different, which is usually the case in practice, because they are of different kinds, it is not possible to fulfill both of these two conditions at the same time and that, if the anode impedance is made real and independent with respect to frequency throughout the frequency range to be reproduced, the frequency characteristic curve is not flat. in other words that linear distortion occurs.

According to the invention this distortion is obviated by providing means by which the oscillations supplied to the control-grid circuit of the amplifying tube are distorted in such -manner that the sound vibrations to be reproduced by the loudspeakers are reproduced practically without distortion.

The invention will be described with reference to the accompanying drawing forming a part of the specification and in which:

Fig. 1 is a schematic diagram of a prior art circuit arrangement,

Fig. 2 is a frequency response diagram of the arrangement shown in Fig. 1,

Fig. 3 is a schematic diagram of the equivalent circuit of the arrangement shown in Fig. 1 from which the basic concept of the invention is de rived, I Fig is a frequency response diagram based on the equivalent circuit of Fig. 3,

. Fig. 5 is a schematic diagram of a circuit arrangement according to the invention, and

Fig. 6' is a schematic diagram of an alternate embodiment of a circuit arrangement according to the invention.

In Fig. 3 there is shown the equivalent circuit of the circuit arrangement shown in Fig. 1, in which it has been assumed that the stray inductances and the losses of the transformers T1 and T2 are negligibly small and that the loudspeaker impedances may be regarded as resistances Brand R2 respectively.

The substitute impedance Z1 of transformer T1 having a transformation ratio nizL and, as has been stated above, a low primary inductance, and of the loudspeaker L1 then consists of the parallel-connection of an inductance L and a resistance n iRi.

It is taken that the impedance of condenser C is always low with respect to the primary inductance of transformer T2, so that the substitute impedance Z2 of this transformer having a transformation ratio 11221, of the loudspeaker L2 and the condenser C consists of the parallel-connection of condenser C and resistance n2 R2.

The adaptation condition is fulfilled if Z1+Z2=constant or if Z1=X1+7'Y1 and Z2=X2+iY2 it is taken that X1+X2=constant (1) Y1+Yz=0 (2) If the acoustic powers radiated by the loudspeakers are designated Waiand Wa2 the electrio powers supplied to them Wei and Wez and their electro-acoustic outputs m and 1 2 Wa1+ Wag must be equal to n1W1+1 2We2= constant in order to fulfill the equalization condition.

Now we have:

where ia represents the anode current of the tube i. If this current is constant for all frequencies, which is the case at a constant control-grid voltage if the internal resistance of tube l is sufiiciently high relatively to the total anode impedance Z1+Z2, the equalization condition may be expressed as follows:

It is obvious that in the case of different outputs m and n2 (2) and (3) are contradictory of one another, so that if the adaptation condition is fulfilled, the equalization condition must remain unsatisfied and that consequently, unless other measures are taken, linear distortion of the sound vibrations reproduced must be tolerated.

In the case of 1 2 this distortion is brought about by a weaker reproduction of the high pitched sounds, as appears from the frequency characteristic curve A shown in Fig. 4 which represents the total acoustic power Wm-l-Waz as a function of the frequency f. In the reverse case n1 a z the frequency characteristic curve has the shape illustrated by curve B in Fig. 4.

According to the invention this distortion is obviated by giving the control-voltage, which is supplied to the grid of tube I, an opposite distortion, for example by supplying the oscillations to be amplified to the grid through a network which brings about a distortion contrary to that represented by the curve A and B respectively. In :the first-mentioned case; this network may, for example, consist of a resistance connected in series with an inductance between grid and cathode and in the second case of a resistance in series with a condenser,

A similar result is obtainable by means of a negative feed-back varying with frequency by including, in the manner illustrated in Fig. 5, a, resistance R1, which is connected in parallel with a condenser C1, in the cathode-lead of the amplifying tube which permits the distortion represented by curve A in Fig. 4 to be eliminated.

If the distortion is determined by curve B, the condenser C1 is replaced by an inductance coil. The negative feed-back varying with frequency has the advantage that at the same time the nonlinear distortion issuppressed.

As an alternative, a negative feed-back can be obtained by providing the transformers T1 and T2 with additional negative feed-back windings having appropriate transformation ratios.

This is carried out in a push-pull amplifier shown in Fig. 6, in which the negative feed-back is obtained by additional negative feed-back windings S1 and $2 on the push-pull transformers T1 and T2.

I What I claim is:

1. An amplifier circuit arrangement for operating a high frequency reproducer in conjunction with a low frequency reproducer having different electro-acoustic characteristics for reproducing a given band of frequencies, comprising an electron discharge tube having an anode, a control grid and a cathode, means to apply a signal voltage having a frequency within said band of frequencies between the control grid and cathode of said tube, a high frequency reproducer, a low frequency reproducer having different electro-acoustical characteristics than said high frequency reproducer, a first transformer having a primary winding and a secondary winding proportioned for optimum transfer of energy to said high frequency reproducer and being coupled thereto, a second transformer having a primary winding and a secondary winding proportioned for optimum transfer of energy to said low frequency reproducer and being coupled thereto, means to connect the primary windings of said transformers in series between the anode and the cathode of said tube, a capacitor shunting the primary winding of said second transformer, said series-shunt circuit having values of inductance and capacity at which the impedance of the circuit is substantially independent of frequency throughout said band of frequencies, and means interposed between the grid and cathode of said tube to apply a potential proportional to the current in said series-shunt circuit in opposition to said signal voltage thereby to produce an acoustic output substantially proportional to said signal voltage.

2. An amplifier circuit arrangement for operating a high frequency reproducer in conjunction with a low frequency reproducer having different electro-acoustic characteristics for reproducing a given band of frequencies, comprising an electron discharge tube having an anode, a control grid and a cathode, means to apply a signal voltage of a plurality of frequencies within said band of frequencies between the control grid and cathode of said tube, a high frequency reproducer, a low frequency reproducer having different electro-acoustical characteristics than said high frequency reproducer, a: first transformer having a primary winding and a secondary winding proportioned for optimum transfer of energy to said high frequency reproducer and being coupled thereto, a second transformer having a primary winding and a secondary winding proportioned for optimum transfer of energy to said low frequency reproducer and being coupled thereto, means to connect the primary windings of said transformers in series between the anode and the cathode of said tube, a capacitor shunting the primary winding of said second transformer, said series-shunt circuit having values of inductance and capacity at which the impedance of the circuit is substantially independent of frequency throughout said band of frequencies, and a shunt combination comprising a resistor and a second capacitor interposed between thegrid and cathode of said tube to apply a voltage proportional to the current in said series-shunt circuit in opposition of said signal voltage to produce an acoustic output substantially proportional to said signal voltage.

3. An amplifier circuit arrangement for operating a high frequency reproducer in conjunction with a low frequency reproducer having different electro-acoustic characteristics for reproducing a given band of frequencies, comprising an electron discharge tube having an anode, a control grid and a cathode, means to apply a signal voltage having a frequency within said band of frequencies between the control grid and cathode of said tube, a high frequency reproducer, a low frequency reproducer having different electro-acoustical characteristics than said high frequency reproducer, a first transformer having two primary windings, a. feedback winding and a secondary winding proportioned for optimum transfer of energy to said high frequency reproducer and being coupled thereto, a second transformer having a center tapped primary winding, a feedback winding and a secondary winding proportioned for optimum transfer of energy to said low frequency reproducer and being coupled thereto, means to connect the primary windings of said transformer in series between the anode and the cathode of said tube,-' the primary winding of said second transformer being interposed between the two primary windings of said first transformer, a capacitor shunting the primary winding of said second transformer, said series-shunt circuit having values of inductance and capacity at which the circuit is substantially independent of frequency throughout said band of frequencies, and means to connect said feedback windings in series between the grid and cathode of said tube to apply a feedback voltage in opposition to said signal voltage to produce an acoustic output substantially proportional to said signal voltage.

4. An amplifier circuit arrangement for operating a high frequency reproducer in conjunction with a low frequency reproducer having different electro-acoustic characteristics for reproducing a given band of frequencies, comprising a first electron discharge tube having an anode, a control grid and a cathode, a second electron discharge tube having an anode and a cathode connected to the cathode of said first tube, means to apply a signal voltage having a frequency within said band of frequencies between the control grid and cathode of said first tube, a high frequency reproducer, a low frequency reproducer having different electro-acoustical characteristics than said high frequency reproducer,

a first transformer having two primary windings, a feedback winding and a secondary winding proportioned for optimum transfer of energy to said high frequency reproducer and being coupled thereto, a second transformer having a center tapped primary winding, a feedback winding, and a secondary winding proportioned for optimum transfer of energy to said low frequency reproducer and being coupled thereto, means to connect the primary windings of said transformers in series between the anodes of said first and said second tubes, the primary winding of said second transformer being interposed between the two primary windings of said first transformer, a capacitor shunting the primary winding of said second transformer, said series-shunt circuit having values of inductance and capacity at which the circuit is substantially independent of frequency throughout said band of frequencies, and means to connect said feedback windings in series between the grid and cathode of said tube to apply a feedback voltage in opposition to said signal voltage to produce an acoustic output substantially proportional to said signal voltage.

GERRIT JAN SIEZEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,635,959 Round July 12, 1927 1,674,683 Hahnemann -1 June 26, 1928 1,698,269 Konheim Jan. 8, 1929 1,711,529 Hahnemann May 7, 1929 1,760,821 Douglass May 27, 1930 

